If you're serious about music and want to know the purpose of a mix engineer and why things are the way that they are, you should read this article about the entire music production process before diving into this one.
The purpose of a mix engineer is to literally mix the instruments together in a way that gives each instrument a unique purpose in a song. In this article, I am going to lay on the table the honest truth about what you should expect when getting your songs mixed and mastered.
Here we go.
What you should expect
First, give them something to go off of.
A "rough mix" is an engineers best friend. It lets them know the direction you want to take your music, the style you're looking for, and what you hope to sound like.
An engineer understands that you're hiring them because you are not happy with the rough mix. So don't spend hours trying to impress the mix engineer, just get it as close as you can to the direction you want and send it off to them.
What should a rough mix include?
Stylizations (auto-tune on vocals, delay, reverb, guitar distortion, etc.)
All the instruments in your song
Notes for what you want but you can't do yourself
If your unable to provide a rough mix, at least compile a list of detailed (and timestamped) notes with what you're going for. Include references to specific songs on Spotify or YouTube that will lead the engineer in the right direction.
Second, expect your song to sound how your rough mix already does... but better.
What this means is that a mixing engineer doesn't try to guess at how you want a song to sound. They take what you sent and work their magic to get it sounding as professional as possible. The rough mix is the place to experiment with how you want to sound. The mixing phase is when the engineer brings your effort in the rough-mix to a polished professional song.
Third, they're going to want stems.
Along with the Rough Mix (which should be a single MP3 or WAV file), you will need to send stems. Stems are the individual tracks of each recording as a separate file without any effects. If you send one mp3 or WAV file of your entire song (the rough mix), the mix engineer won't really be able to do much with it. You know you're doing it right when you're sending a folder filled with audio files for each instrument without any effects.
Click here to watch a video that guides you through exactly how to send stems to us.
Fourth, nothing beats a solid take.
It's true, nothing can make a better mix like a better take. The biggest mistake artists make during the production process is believing this thought "it will be fixed in mixing". It's probably not true.
Let me describe what IS fixed in a mixing:
Song feeling muddy or overcrowded because of instruments being too "busy".
Vocals not feeling frontal or powerful enough.
Song or particular instruments feeling too loud or too quiet.
These 3 things make a HUGE difference, which is why mixing is so important. But if you're tempted to think that any other problem will be fixed, I urge you to say instead "y'know what, I can record a better take".
Fifth, revisions are key to getting the sound you want but it's not the time to experiment.
Engineers expect one or two revisions. A good mixing engineer understands that music is stylistic and it's unlikely they will nail exactly what you want on the first draft (but sometimes they do). Don't be afraid to ask the engineer to "bring the vocals out a bit more" or "have the guitar sit a little softer in the mix".
Although revisions are key, it's not the stage to be experimental. That should have happened earlier in the production or tracking stage (rough mix). A mixing engineer is hard-focused on mixing the instruments together to sound good together. Asking a mix engineer to "add autotune" or "try some more delay and reverb here" when you hadn't included that in your original rough-mix or notes will frustrate them as it is simply not their job or expertise.
Summary and Conclusion
Everyone on our team wants you to LOVE your song. As the artist, you know better than anyone else how you want it to come out. Be the great leader that creates a clear roadmap for the mixing engineer by:
Having a finished rough-mix (or at least detailed and timestamped notes)
Expect the mix engineer to follow your rough mix (they won't "fix" your song)
Send organized stems
Supply quality recordings
Revise until perfected, productively (don't ask the mix engineer to be a producer)
If you do these things well, you can expect a song that sounds exactly how you imagined... but better.